Myth: First-price auctions made everyone overpay

Myth: First-price auctions made everyone overpay

The folk story is that when exchanges flipped from second-price to first-price around 2017-2019, buyers got fleeced — you now pay your full bid instead of the runner-up's price plus a cent.

Let's trace the actual mechanism.

1. In a true second-price auction (winner pays the second-highest bid + 0.01), the dominant strategy is to bid your true valuation. There's no penalty for honesty.

2. The catch: most "second-price" exchanges were never clean. Soft floors, fee-laden reserve prices, and unobservable publisher-side rules meant you often paid close to your bid anyway. The audit was impossible because you couldn't see the clearing logic.

3. First-price (you pay exactly what you bid) forces a behavioral change called bid shading — the DSP lowering your submitted bid toward the expected clearing price, estimated from won/lost log data.

4. Net effect: a well-calibrated shading model in first-price often clears lower than the murky second-price world it replaced, because now the clearing price is observable and the model optimizes against it.

The transition didn't raise prices structurally. It moved price discovery from the seller's hidden ledger into the buyer's model, where you can actually measure it.

Why it matters: blaming first-price for high CPMs usually means your shading is mistuned, not that the auction format is robbing you.